Polyurea foam compositions are relatively recent innovations in the foam art which have a relatively low density (about 0.5 lb/ft.sup.3 ; 8 kg/m.sup.3). These polyurea foams were developed mostly for use as retrofit insulation, show much greater resistance to ignition by small-scale sources than previously known urethane foams of the same low density, and are usually produced by reacting a polymeric isocyanate, especially a polyphenyl polymethylene polyisocyanate, and an aqueous activator formulation, the essential ingredients of which are water and a catalyst. Significant latitude in mixing ratio of polymeric isocyanate to water (e.g., 7.5:1 to 3:1, equivalent weight basis) is possible in these polyurea foam compositions, giving a wide range of reactivity values with little change in physical properties of the foam.
The original polyurea foam aqueous activator formulation comprised the following:
______________________________________ Ingredient Parts by Weight ______________________________________ H.sub.2 O 15 2-methylimidazole 4 Pluracol .RTM. 492(L-61) 0.25 (surfactant) ______________________________________
This aqueous activator formulation had a number of deficiencies in its process and handling parameters. Specifically, this formulation was very corrosive (having a pH of about 10), had a tendency to form polyurea foam base holes (large voids at the base of a foam container), and the 2-methylimidazole catalyst had a tendency to crystallize out of solution at temperatures below 10.degree. C.
More recently, an improved aqueous activator formulation has comprised the following:
______________________________________ Ingredient Parts by Weight ______________________________________ H.sub.2 O 15 2-methylimidazole 2.0 1,2-dimethylimidazole 1.0 Boric acid 1.0 Pluronic .RTM. L-62.sup.1 0.25 Sodium mercaptobenzothiazole 0.02 ______________________________________ .sup.1 Pluronic .RTM. L-62 = Poly(oxyethylene)poly(oxypropylene); BASFWyandotte
Such an aqueous activator formulation, while containing additional components, gives better processing latitude in making the polyurea foam, is storage stable to 0.degree. C., and is much less corrosive to commonly used storage and process equipment materials.
Considerable development work by others in varying ratios of reactants in formulations has been done to determine the effects of polyol addition and the effects of various flame retardants in these polyurea foam compositions. Such results are shown by the following tables.
______________________________________ EFFECTS OF POLYOL ADDITION ______________________________________ H.sub.2 O 21 21 21 Fyrol CEF.sup.1 30 25 15 2-MI.sup.2 4 4 4 LG-168.sup.3 -- 10 21 RUBINATE-M.sup.4 100 100 100 Cream 14 13 14 End Rise 65 70 80 Density (Kg/m.sup.3) 6.4 6.3 6.7 Bunsen Test Very Good Good Fair ______________________________________ N.B. CEF added to activator which gave unstable emulsion. Addition to isocyanate (stable mixture) showed no change in results. Substitution of Fyrol PCF for CEF resulted in coarser texture and reduced resistance to ignition. .sup.1 Fyrol CEF = tris(betachloroethyl)phosphate; Stauffer Chem. Co. .RTM.- .sup.2 2 MI = 2methylimidazole .sup.3 LG-168 = poly(oxypropylene) adduct of glycerol; Union Carbide Corp .RTM.- .sup.4 Rubinate M = polymeric isocyanate; Rubicon Chem. Co. .RTM. (polyphenyl polymethylene polyisocyanate)
______________________________________ EFFECTS OF VARIOUS FIRE RETARDANTS ______________________________________ Fyrol CEF 30 .fwdarw. 45 pbw. Reduced friability, increased resistance to ignition. Substitute 1,2 DMI.sup.1 (2 pbw) Slight shrinkage, reduced for 2 MI (4 pbw) physical properties. Inclusion of NH.sub.4.sup.+ salts Ammonium Sulphonate Collapse Ammonium Bromide Collapse Diammonium hydrogen phos- Partial collapse, coarse. phate Vircol 82.sup.2 prepolymer Fine texture, slight shrinkage, reduced ignition resistance. Chlorinated Paraffins Partial collapse, coarse. ______________________________________ N.B. Choice of organic fire retardants is critical. Those that promote formation of oil in water emulsions during mixture of the activator and isocyanate usually result in collapsed foams. This is due to loss of blowing agent through the continuous phase. .sup.1 1,2 DMI = 1,2dimethylimidazole .sup.2 Vircol 82 = phosphoruscontaining polyol, 11.3% P; Mobil Chemical Co. .RTM.-
__________________________________________________________________________ EFFECTS OF RATIO AND CATALYST LEVEL CHANGES Sample (1) (2) (3) (4) (5) (6) (7) (8) (9) __________________________________________________________________________ H.sub.2 O (pbw) 15.0 22.6 25.0 28.2 37.3 28.8 29.2 29.6 31.05 2-methyl Imidazole 2.0 3.0 2.0 3.8 5.0 3.4 3.2 2.85 1.9 1,2-dimethyl Imidazole 1.0 1.5 1.0 1.9 2.5 1.7 1.6 1.42 .95 Boric Acid (Tech) 1.0 1.5 1.0 1.9 2.5 1.9 1.9 1.9 1.9 Pluronic L-62 .RTM. 0.25 0.38 .25 .47 .62 .47 .47 .47 .47 Sodium Mercapto Benzothiazole (NAMBT) 0.02 0.03 .02 .036 .048 .036 .036 .036 .036 Fyrol CEF .RTM. 45.0 45.0 45.0 45.0 45.0 45.0 45.0 45.0 45.0 RUBINATE-M .RTM. 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 Ratio (Iso/Activator) 7.5/1 5/1 7.5/1 4/1 3/1 4/1 4/1 4/1 4/1 Reactivity (sec.) Cream 12 7 16 6 5 8 9 10 21 End Rise 72 40 65 50 35 57 67 75 130 Tack Free 75 40 60 50 35 57 67 75 155 Density (lb/ft.sup.3) .41 .43 .50 .40 .48 Exotherm (40" .times. 300.degree. F.6") 192.degree. F. 190.degree. F. -- 185.degree. F. -- 180.degree. F. Comments: scorch no excess no no 10% 17% -25% -50% scorch H.sub.2 O on scorch scorch catalyst fine 5/1 fine fine removed cell no cell cell scorch softer ratio retained by H.sub.2 O addition base than no slightly coarse holes (1) scorch coarse RMC ($/lb) 2/1/77 0.63 0.66 0.62 __________________________________________________________________________
However, the foregoing foam compositions are more dense than desired for some applications. Those in the art continue to study to learn how to produce less dense polyurea foam compositions which retain substantial compressive strength and flame-retardant properties in an economical manner. In other cases, compressive strength is less than desired and could well be improved.